Method of holding substrate and substrate holding system

ABSTRACT

A method and system of holding a substrate where foreign substances on the back surface can be decreased. The substrate holding system comprises a ring-shaped leakage-proof surface having a smooth surface on the specimen table corresponding to the periphery of the substrate, a plurality of contact holding portions within the periphery of the substrate, and electrostatic attraction means for fixing the substrate by contacting the back surface of the substrate to the ring-shaped leakage-proof surface and the contact holding portions. The substrate contacts to the cooling surface at the ring-shaped leakage-proof surface and the contact holding portion placed on a position inside the ring-shaped leakage-proof surface. The back surface of the substrate and the cooling surface do not contact to each other in the large portion of the remaining area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/778,780,filed Feb. 8, 2001, which is a continuation of application Ser. No.09/109,178, filed on Jul. 2, 1998 now U.S. Pat. No. 6,336,991 ), whichis a continuation of application Ser. No. 08/904,623, filed on Aug. 1,1997 now U.S. Pat. No. 5,961,774, which is a continuation of applicationSer. No. 08/670,180, filed on Jun. 20, 1996, now U.S. Pat. No.6,048,434, which is a divisional of application Ser. No. 08/307,238,filed on Sep. 16, 1994 now U.S. Pat. No. 5,792,304; the entiredisclosures of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method of holding a substrate and asubstrate holding system to hold a substrate securely during aproduction process for treating the substrate, such as semiconductordevice, while it is being cooled.

Among substrate treating apparatuses for production of semiconductordevices, there are a lot of substrate treating apparatuses requiring thecooling substrates, such as a plasma treatment apparatus, a sputteringapparatus, a dry etching apparatus, a CVD (chemical vapor deposition)apparatus and a high energy ion implantation apparatus. Since thetreating environment in these apparatuses is generally a vacuum, it isdifficult to cool a substrate by bringing it into contact with a coolingsurface, as in atmospheric pressure, because of the decrease in thermalconductivity which occurs in a vacuum. Although there is abundantliterature concerning thermal conductivity in a vacuum (rarefied gas),the amount of heat transferred by contact is small because of the smallreal contact area when surfaces come into contact with each other.Especially in heat transfer between a substrate and a cooling surface,it is difficult to strongly press the substrate against the coolingsurface since there is a possibility to damage the substrate. Therefore,various ideas, such as placing a soft elastomer on the surfacecontacting the substrate, have been proposed. However, in recent years,it has been more conventional for a gas to be introduced between thesubstrate and a cooling surface to cool the substrate using the gas as acoolant, when the heat load in the substrate increases or a requirementto cool the substrate to lower the temperature thereof arises.

There are various types of gas cooled substrate holding systems. Theycan be roughly categorized as follows: (1) a gas cooling type systemwhere the back surface of a substrate and a cooling surface contact eachother and a gas is introduced into the gap between the surfaces formedby the surface roughness, and (2) a gas cooling type system where theback surface of a substrate and a cooling surface do not contact eachother and a gas is introduced into the gap between the surfaces.

The prior art gas cooling type systems belonging to the former category(1) are described in, for example, Japanese Patent Publication No.2-27778 (1990), Japanese Patent Application Laid-Open No. 62-274625(1987), Japanese Patent Application Laid-Open No. 1-251375 (1989),Japanese Patent Application Laid-Open No. 3-154334 (1991) and JapaneseUtility Model Application Laid-Open No. 4-8439 (1992). And, the priorart gas cooling type systems belonging to the latter category (2) aredescribed in, for example, Japanese Patent Application Laid-Open No.63-102319 (1988), Japanese Patent Application Laid-Open No. 2-312223(1990), Japanese Patent Application Laid-Open No. 3-174719 (1991).Further, there is another type of system, described in Japanese PatentApplication Laid-Open No. 2-30128 (1990), where, before introducing acooling gas, the back surface of a substrate and a cooling surface arebrought into contact with each other, but during cooling the substrateis pushed up due to gas pressure caused by introducing the cooling gasand does not contact the cooling surface.

In these cooling systems, providing that a certain cooling gas is used,the cooling capacity (magnitude of transferred heat) with the coolinggas depends on the pressure of the gas and the distance between the backsurface of a substrate and the cooling surface (gap in the back surfaceof the substrate). FIG. 8 schematically shows the characteristic ofthermal conductivity in a low pressure situation. When the pressure ofthe cooling gas is low, the amount of transferred heat is proportionalto the pressure of the cooling gas and independent of the magnitude ofthe gap between both of the surfaces. When the pressure of the coolinggas is higher than the pressure PO, where the mean free path of thecooling gas nearly coincides with the gap, the amount of transferredheat becomes constant and independent of the gas pressure. The pressureof the cooling gas in the type of system in category (1) described aboveis generally in the region where the heat transfer is proportional topressure, and the pressure of the cooling gas in the type of system incategory (2) described above is generally in the region where the heattransfer is independent of pressure.

Characteristics and problems in various methods of cooling a substratewill be described below.

First, a description will be made on the case where cooling is performedunder a condition that a substrate contacts a cooling surface. Thecooling methods belonging to this type are disclosed in Japanese PatentPublication No. 2-27778 (1990), Japanese Patent Application Laid-OpenNo. 62-274625 (1987), Japanese Patent Application Laid-Open No. 1-251375(1989), Japanese Patent Application Laid-Open No. 3-154334 (1991) andJapanese Utility Model Application Laid-Open No. 4-8439 (1992). In thecooling method of this type, although the substrate and the coolingsurface contact each other, only the most protruding portions on thecooling surface contact the substrate when it is observed in detail. Theindented portions on the cooling surface and on the substrate do notcontact each other, and the gaps are approximately 10 μm to 50 μm,although this depends on the surface roughness. In a case where acooling gas is introduced in the gap, the pressure is generally severalTorrs, which is in a region nearly equal to the mean free path.Therefore, a sufficient cooling efficiency can be obtained by properlysetting the pressure as shown in FIG. 8.

However, when the cooling gas is supplied from a specified singleportion, as shown in the figure in Japanese Patent Publication No.2-27778 (1990), the pressure is highest in the cooling gas supplyingportion and decreases as it goes toward the peripheral portion of thesubstrate. Since the cooling efficiency has a pressure dependence asshown in FIG. 8, there arises a disadvantage that uniformity of thetemperature distribution is deteriorated due to the non-uniformity ofthe cooling efficiency. If there is no gas leakage, that is, no gasflow, the pressure distribution does not occur and the temperaturedistribution becomes uniform. However, in order to achieve this, theperipheral portion of the substrate needs to be shielded. This isdescribed in Japanese Patent Application Laid-Open No. 62-274625 (1987)or in Japanese Utility Model Application Laid-Open No. 2-135140.Further, the method in which cooling gas is supplied from pluralportions to make the pressure distribution on the back of the substrateuniform is described in Japanese Patent Application Laid-Open No.1-251735 (1989) or in Japanese Patent Application Laid-Open No. 4-61325(1992). In any case, in these cooling methods, since the back surface ofthe substrate and the cooling surface contact each other in a largearea, there is a disadvantage in that a lot of foreign substances becomeattached to the back surface of the substrate when contacting thecooling surface. Further, in order to prevent the cooling gas fromleaking through the peripheral portion of the substrate using ashielding material, a load for the shielding needs to be applied.Therefore, a way of tightly fixing the substrate in some manner isrequired.

Description will be made below of a cooling method where a substrate anda cooling surface do not contact each other and a cooling gas issupplied into the gap. The prior art method is described in JapanesePatent Application Laid-Open No. 3-174719 (1991) or in Japanese PatentApplication Laid-Open No. 4-6270 (1992), in which a substrate ismechanically fixed to a cooling surface from the top surface or the sidesurface of the substrate. Since the substrate, in these examples, ismechanically fixed, there is a disadvantage that foreign substances areapt to be produced at the fixing portion. In the methods described inJapanese Patent Application Laid-Open No. 63-102319 (1958) and inJapanese Patent Application Laid-Open No. 2-30128 (1990), a substrate isnot fixed specially, but is held by the weight of the substrate itself.In this case, in order that the leakage of the cooling gas is notincreased too much or the substrate is not caused to float up, thepressure of the cooling gas has to be limited to a low level. Thiscauses a disadvantage in that the cooling efficiency is decreased.

Electrostatic adhesion is a known method of fixing a substrateelectrically. An example where a substrate is fixed to a cooling surfacewith this method and projections are provided on the periphery of thesubstrate is described in Japanese Patent Application Laid-Open No.62-208647 (1987). A substrate contacts a cooling surface only at aplurality of projections provided in separate spaced relation on theouter periphery and inner periphery of the substrate, which is describedin the Japanese Patent Application Laid-Open No. 62-208647 (1987). And,this publication indicates that cooling gas easily leaks and that theadhering force is unstable. Further, in order to improve this method, itis effective if the outer periphery is not projected and the projectionsare provided only on the inner peripheral portions, and further, if theprojections in the inner periphery are provided in the central portion,instead of in separate spaced relation. In this case, the gap betweenthe substrate and the cooling surface becomes non-uniform over thesurface of the substrate, which causes a non-uniform pressuredistribution on the back surface of the substrate. When the gap betweenthe back surface of the substrate and the cooling surface varies fromone position to another, the ratio of the mean free path of the coolinggas and the gap has an uneven distribution over the surface of thesubstrate. Therefore, a disadvantage arises in that the temperaturedistribution is apt to become large due to the difference in coolingefficiency, as can be understood from FIG. 8, even if the pressuredistribution is not so large. In the electrostatic adhering methoddescribed in this example, there are provided positive and negativeelectrodes on the cooling portion to which a direct current high voltageis applied to produce an electrostatic adhering force. In theelectrostatic adhering method of this type, there may arise adisadvantage in that, when a substrate is treated in a plasma, theelectric charge on the surface of substrate produced by irradiated ionsor electrons is apt to be non-uniform, and so a current flows on thesurface of substrate to damage the substrate.

Each of the conventional technologies, as described above, has the mainobjective of cooling a substrate efficiently. However, with an increasein integration of semiconductor devices in recent years, it is requiredto decrease the amount of small foreign substances, such as particles ordust and heavy metal impurities, to less than the allowable limit in thepast. The same can be said for foreign substances attached on the backsurface of a substrate. When the amount of foreign substances attachedon the back surface of a substrate is large, there arises a disadvantagein the next process in that the foreign substances on the back surfaceare attached to the top surface of an adjacent substrate, or are removedfirst from the substrate and attached to another substrate. Therefore,decreasing the amount of foreign substances is an important problem forstabilizing the semiconductor production process or improving the yield.Attaching of foreign substances on the back surface of a substrateoccurs by contacting the back surface of the substrate to anothermember. Therefore, a lot of foreign substances are attached to asubstrate by contacting a cooling surface for the substrate.

Further, the prior art does not refer to the consideration of substratesize. Although it is mentioned that the influence upon the process islessened by leaking cooling gas into the treating chamber, with theadhering force being as small as possible, the relation between theadhering force and the cooling gas pressure is not mentioned.

A conventional substrate holding system in a substrate etching apparatusgenerally employs a method in which a substrate is pressed along itsperiphery with hooks, as described in Japanese Patent ApplicationLaid-Open No. 2-148837 (1990) or Japanese Patent Application Laid-OpenNo. 2-267271 (1990). When there is such a member contacting the surfaceof the substrate, problems arise in that the contact portions in thesubstrate are obstructed by the etching, the contacting member itselfbeing also etched to some extent together with the substrate. As aresult, the foreign substance sources, such as reaction products, areattached to the contacting member and the contacting member may bedamaged, which may lead to production of foreign substances.

On the other hand, in a substrate holding method in which a substrate isheld using electrostatic force (hereinafter, referred to as“electrostatic adhering”), as described in, for example, Japanese PatentApplication Laid-Open No. 2-135753 (1990), a substrate is placed on anelectrostatic adhering portion made of a dielectric material and a highvoltage is applied to hold the substrate with an electrostatic adheringforce. In this case, there is no special member to press the substratein the periphery of the substrate. Therefore, the problem of thepossibility of producing foreign substances as described in the aboveexample is solved. However, the positional relationship between thesubstrate and the electrostatic adhering member is such that thesubstrate is placed in the uppermost position (substrate etching spaceside) and a step is formed in the electrostatic member such that theelectrostatic adhering member comes to be placed below the substrate.When such a step exists, gas flow during etching a substrate changesabruptly at the periphery of the substrate to cause a non-uniformetching in the substrate in some cases.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of holding asubstrate and a substrate holding system in which the amount of foreignsubstances on the back surface can be decreased, and only a small amountof foreign substances may be transferred from a mounting table to asubstrate.

Another object of the present invention is to provide a method ofholding a substrate and a substrate holding system where the deformationin a large diameter substrate can be suppressed, and the coolingefficiency for the substrate can be kept sufficiently high.

A further object of the present invention is to provide a method ofholding a substrate and a substrate holding system in which damage tothe substrate caused during treating the substrate can be prevented.

A still further object of the present invention is to provide a methodof holding a substrate and a substrate holding system in which a coolinggas can be quickly dispersed over the back surface of a substrate whenthe cooling gas is introduced, after the substrate is electrostaticallyattracted, and substrate temperature control suitable for highproductivity can be performed.

Another object of the present invention is to improve the product yieldof substrate etching and the availability of the substrate etchingapparatus providing a substrate holding system which is subjected to areduced amount of foreign substances as described above and is capableof performing uniform etching.

According to the present invention, there is provided a ring-shapedleakage-proof surface having a smooth surface on the specimen tablecorresponding to the periphery of the substrate, a plurality of contactholding portions which bear against and support the substrate on thespecimen table between the corresponding position to the periphery ofthe substrate and the corresponding position to the center of thesubstrate, and electrostatic attraction means for generating anelectrostatic attraction force to attract the substrate toward thering-shaped leakage-proof surface and the contact holding portions.

In order to decrease the amount of foreign substances which may adhereon a substrate, it is effective to decrease the contact area between acooling surface and a substrate. However, the distance between thecooling surface and the back surface of the substrate needs to be keptat a distance so as not to decrease the cooling efficiency of a coolinggas. In order to realize this, a small high step is provided on thecooling surface, such that the back surface of the substrate and thecooling surface do not contact each other whether the cooling gas isintroduced or not. Although the cooling surface and the back surface ofthe substrate contact each other at protruding portions provided on thestep portion of the cooling surface, the area of the contact portionsneeds to be limited so as to be as small as necessary. In the presentinvention, therefore, an electrostatic attraction function is given tothe cooling surface to attract the substrate to the protruding portionsof the cooling surface.

Prevention of leakage of the cooling gas has to be considered. Accordingto the present invention, this can be attained by providing aring-shaped protruding portion having a smooth surface, that is,leakage-proof surface, on the cooling surface corresponding to theperipheral portion of a substrate, and fixing the back surface of thesubstrate to the cooling surface with electrostatic adhesion to preventthe cooling gas from leaking.

According to the present invention, the following effects are obtained.One of the effects is a solution for the problem concerning thetransportation of foreign substances in a pusher portion relating tohandling of the substrate. The pusher provided inside or through amounting table contacts other members and cannot avoid a foreignsubstance source. In the present invention, the excess cooling gas flowstoward the opposite side of the mounting table through the hole. Sincethe foreign substances produced are carried in the opposite direction tothe substrate, the amount of foreign substances attached to thesubstrate is decreased.

Another effect of the present invention is that a cover is provided inthe back surface of the mounting table to protect the mechanism in theback surface of the mounting table from being contaminated by reactionproducts over a long time of use as much as possible. Since complexmechanisms, such as the coolant supplying system and the verticaldriving mechanism for the mounting table, are usually constructed in theback of the mounting table, it is troublesome when the reaction productsproduced by etching attach to these parts. In order to avoid this,according to the present invention, a cover is provided in the backsurface of the mounting table such that the excess cooling gas flowsinto the inside of the cover, the pressure inside the cover being kepthigher than the pressure in the treatment chamber during treating tosuppress the reaction products from entering the treatment chamber,which protects the mechanism in the back surface of the mounting tablefrom contamination by reaction products over a long time of use.

The prevention of damage to the substrate can be attained by connectingthe electric circuit for electrostatic adhesion from the substrate sideto a grounded part, such as the vacuum chamber, through the plasma tominimize the electric potential over the surface of the substrate.

According to the present invention, a substrate contacts a coolingsurface at a ring-shaped leakage-proof surface and at contact holdingportions positioned inwardly of the ring-shaped leakage-proof surface.However, since the back surface of the substrate does not contact thecooling surface in most of the remaining part of the area, attaching offoreign substances caused by contact can be prevented. Although thecooling efficiency for the substrate cooling is decreased a littlecompared to when the substrate contacts the cooling surface under thesame pressure of the cooling gas, a sufficient cooling efficiency can beobtained by forming a step on the cooling surface smaller thanapproximately 100 times the mean free path of the cooling gas. The gapbetween the back surface of the substrate and the cooling surface islarge in comparison to that in the conventional cooling method, wherethe substrate and cooling surface contact each other over the wholesurface. Therefore, the conductance between both surfaces is large sothat supplying and exhausting of cooling gas are easily performed. Thatis, the time to supply and exhaust the cooling gas is short, and so thetime for treating a substrate can be shortened. Further, there is afunction that the conductance at the contact portion of the periphery ofthe substrate and the cooling surface is very small in comparison to thenon-contact portion of the inner portion of the substrate (in themolecular flow region, the conductance is proportional to the square ofgap), the pressure difference across the non-contact portion beingsmall, that is, the cooling efficiency being uniform.

When the substrate temperature is controlled using a cooling gas as acoolant, the pressure of the cooling gas is required to be higher than 2Torrs. And, the higher the pressure is, the higher the efficiency ofheat transfer becomes. On the other hand, the electrostatic adheringforce largely depends on the temperature of the substrate beingcontrolled. In a typical production line today, the temperature isapproximately −60° C. to +100° C., and an adhering force of 40 to 100gf/cm² is stably obtained under an applied voltage in general of 300 to1000V. Concerning the pressure control of the cooling gas, it isdifficult to control the pressure precisely, since the pressure largelychanges depending on the time constant of the gas supplying system orthe relationship between the relative roughnesses of the contactsurfaces of the substrate and the mounting table. Therefore, the targetof the pressure control may be, for example, 10 Torrs±5 Torrs.

When the outer periphery of the substrate is fixed by adhesion with theconventional method and a gas is filled in the back of the surface withthe pressure of 10 Torrs, the substrate is deformed by 0.1 to 0.25 mm.This magnitude of deformation degrades the work accuracy of substrateetching as well as lessens the heat transfer efficiency of the coolinggas. To solve this problem, adhering portions are additionally providedon the center side of a substrate, for example, one ring-shaped adheringportion for a 6″ substrate, two ring-shaped adhering portions for an 8″substrate, in addition to the adhering portion on the periphery of thesubstrate. Therewith, the deformation can be prevented.

It is well known that when a substrate contacts another member, foreignsubstances are certainly attached to the contact point. From this pointof view, it is clearly preferable that the electrostatic adheringsurface is small. However, taking the pressure control level andadhering force into consideration as described above, it is suitable inthe up-to-date technical level that the adhering area is less thanapproximately half of the total area of the substrate. This is because,when the electrostatic adhering force is 40 gf/cm₂ and the adhering areais half of the total area, the total adhering force for an 8″ substratebecomes approximately 6280 gf, and the separating force with the coolinggas of 15 Torrs is approximately 6100 gf.

Further, by providing a pusher for substrate transportation in a holepenetrating the back surface of the mounting table, the excess coolinggas serves as a carrier gas for carrying foreign substances produced atthe pusher portion to prevent the foreign substances from attaching tothe substrate. In addition to this, the excess cooling gas is introducedinto the inside of a cover on the back surface of the mounting table andmakes the pressure inside the cover higher than the pressure in thetreating chamber to prevent contamination of and attaching of reactionproducts to the mechanisms on the back of the mounting table.

In order to prevent abnormal discharge from occurring when the highfrequency voltage is applied to the substrate to generate a bias voltagefor etching the substrate, a high frequency voltage applying portion anda standard electric potential portion are insulated with an electricalinsulating material so as not to face each other directly. In additionto the above measures, a pin for transporting the substrate is providedand is constructed so as to be electrically conductive. Since theelectrostatic adhering force due to a remaining charge can beinstantaneously dissipated by removing the charge accumulated in thesubstrate by causing the pin to contact the substrate when the substrateis transported, the substrate is not lifted with unnecessary force.

Since the flow passage to conduct the coolant for controlling thetemperature of the substrate is formed by diffusion welding or solderingin such a structure that the portion forming the flow passage iscompletely jointed, no seal is required when a through hole is providedin any place except the flow passage. Therefore, a temperature detectoror a detector for detecting the presence or absence of substrate can beeasily provided.

In order to make the gas flow on the surface of a substrate uniformly, agas flow controlling member (hereinafter referred to as a “susceptor”)is provided in the outer peripheral portion of the substrate. Thesurface of the susceptor is at a higher level than that of the substrateso that the gas flow does not abruptly change direction at the peripheryof the substrate. The surface of the susceptor facing the periphery ofthe substrate is formed normal to the surface of the substrate torestrict movement in the lateral direction or sliding of the substrate.Further, there are some cases in which the reaction products produced bysubstrate etching or the plasma flows into the gap between the covermember facing the back surface of the substrate in the peripheralportion and the back surface of the substrate to cause foreignsubstances to attach on the back surface of the substrate. Thisphenomena is prevented by the distance between the back surface of thesubstrate and the cover, member.

As described above, since contact between a foreign substance source anda substrate is eliminated as far as possible, the transfer of foreignsubstances to the substrate can be decreased. Further, since the gasflow is made uniform, the uniformity in the substrate etching over thesurface can be improved. Since the detector for measuring substratetemperature and the detector for detecting the presence or absence of asubstrate can be easily installed by modification of the structure andthe manufacturing method of the substrate holding system, thereliability and the operability of the apparatus can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view showing an outline of asubstrate treatment apparatus to which a substrate holding system inaccordance with the present invention is applied.

FIG. 2 is a vertical cross-sectional view showing an embodiment of thesubstrate holding system in FIG. 1.

FIG. 3 is a vertical cross-sectional view showing another form of thesubstrate holding system to be used in the apparatus of FIG. 1.

FIG. 4 is a top plan view showing the substrate holding system in FIG.3.

FIG. 5 is a top plan view showing another substrate holding system.

FIG. 6 is a top plan view showing a further substrate holding system.

FIG. 7 is a vertical cross-sectional view showing another substrateholding system in accordance with the present invention.

FIG. 8 is a view explaining the heat transfer characteristic in avacuum.

FIG. 9 is an explanatory view showing another substrate holding systemin accordance with the present invention.

FIG. 10 is an explanatory view showing a substrate etching apparatushaving a substrate holding system in accordance with the presentinvention.

FIG. 11 is an enlarged view showing the outer peripheral portion of thesubstrate holding system of FIG. 9.

FIG. 12 is an explanatory view showing removing accumulated chargeduring transporting a substrate.

FIG. 13 is a vertical cross-sectional view showing another substrateholding system in accordance with the present invention.

FIG. 14 is an explanatory view showing a method of manufacturing thecoolant flow passage in the substrate holding system of the presentinvention.

FIG. 15 is an explanatory view of another substrate holding system.

FIG. 16 is an explanatory view of the coolant flow passage of a holdingmember in FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As a first embodiment according to the present invention, FIG. 1 showssubstrate treatment apparatus employing an electrostatic adheringcircuit for fixing a substrate 1 to a substrate holding system 9. InFIG. 1, a microwave plasma etching apparatus is used for treating thesubstrate 1. A substrate holding system 9 mounting the substrate 1 isplaced in an etching chamber 10. The etching chamber 10 is exhaustedusing a vacuum pump 11, and a gas for etching is supplied from a gassupply unit. The substrate holding system 9 is connected to a highfrequency power source 12 and a direct current power source 13.Microwave energy is introduced into the etching chamber 10 from a quartzglass window 15 through a waveguide 14. When the high frequency powersource 12 is switched into operation or the microwave is introduced, aplasma 16 is produced in the etching chamber 10. At that time, anelectrostatic adhering circuit 17 is formed by the potential of thedirect current power source 13 through the substrate holding system 9,the substrate 1, and the plasma 16. In this state, the substrate 1 isfixed to the substrate holding system 9, that is, fixed by theelectrostatic force produced in the substrate holding system 9.

FIG. 2 shows a cross-section of the substrate holding system 9 inFIG. 1. A substrate 1 is mounted on protruding portions 3 and 20 of aholding member 2 for holding the substrate, the protruding portion 3 ofthe holding member 2 being connected in the electrostatic adheringcircuit 17, the substrate 1 being fixed to the holding member 2 at theportions 3 and 20. A flow passage for supplying a coolant 4 is providedin the holding member 2 to cool the substrate 1. The coolant is suppliedfrom a supplying unit to an inlet portion 5, schematically illustrated,and flows out from an outlet portion 6 to control the temperature of theholding member 2. Further, a flow passage for a cooling gas 7 isprovided in the center of the holding member 2 to supply and exhaust thecooling gas 7. The temperature control of the substrate 1 is attained bythe cooling gas 7 which flows into the indented portion 8 of the holdingmember 2 so as to perform a heat transfer between the holding member 2and the substrate 1. The electrostatic adhering force is generated by adielectric material 18 attached to or formed on the surface of theholding member 2.

Aluminum oxide, or mixture of aluminum oxide added to titanium oxide,may be used as the dielectric material 18. A voltage of several hundredvolts is applied to the holding member as a direct current voltage forgenerating the electrostatic force. Therewith, the substrate iselectrostatically fixed to the protruding portion 3 of the holdingmember 2 shown in FIG. 2. The electric potential for electrostaticadhering is applied from the direct current power source 13, thepotential being uniform over the holding remember 2, over the protrudingportion 3 and over the outer periphery of the substrate 1. Therefore,the potential difference produced over the surface of the substrate 1 iscaused by the distribution of electrons or ions irradiated on thesubstrate 1, and is not so high that the potential difference may causedamage to the substrate 1. On the other hand, in a method where positiveand negative electric poles are formed in the holding member 2 to causethe substrate to adhere electrostatically with the electric poles, thereis a possibility that a high voltage difference in the substrate 1 willgive rise to damage to the substrate.

Then, the cooling gas 7 is supplied to the back surface of the substrate1 fixed in such a manner. The cooling gas 7 fills in the indentedportion 8 of the holding member 2, the pressure being within the rangeof several Torrs to several tens of Torrs. When the gap of the indentedportion 8 is 15 μm to 0.1 or 0.2 mm, a decrease in the coolingefficiency can be neglected. That is, the gap needs to be larger than15μ when the existence of particles or the roughness of surface isconsidered, and the upper limit of the gap is 0.2 mm when the thermalconductance of the gas is considered.

It can be considered that the electrostatic adhering force is nearlyzero over the indented portion 8 where there is a gap, and is generatedonly over the protruding portion 3. However, since it is possible to setthe adhering force strong enough to endure the pressure of the coolinggas 7 by properly setting the voltage of the direct current power source13, the substrate 1 is not moved or separated by the cooling gas 7.

The temperature of the holding member 2 is controlled by the coolant 4.Therefore, the molecule of the cooling gas 7 cooled on the surface ofthe indented portion 8 of the holding member reaches the substrate 1directly or after any number of collisions with other molecules of thecooling gas. The molecule of the cooling gas which has reached thesubstrate 1 receives energy from the substrate 1, that is, cools thesubstrate 1, returning again to the holding member to transfer the heatit carries thereto. By repeating this cycle, the substrate 1 is cooled.In the case where the pressure of the cooling gas 7 is sufficientlyhigher than the pressure which establishes the mean free pathcorresponding to the gap at the indented portion 8, it becomes adominant phenomenon that the gas molecules collide and exchange energywith each other to carry the thermal energy in the substrate 1 to thecooling surface of the holding member 2 in addition to theabove-described phenomenon of the gas molecules. However, the thermalenergy transport within the range of the present invention involves heatconduction through the cooling gas 7 as a thermal medium. In otherwords, it is not the phenomenon where, for example, the cooling gas 7 iscooled using a cooling unit separately provided in advance and issupplied to the back surface of the substrate 1 to cool the substratewith the heat capacity of the gas itself. Rather, the gas merely acts asa transport medium for the thermal energy. The gap of the indentedportion 8 and the pressure of the cooling gas 7 satisfying the abovecondition are chosen.

The ratio of energy transport between the cooling gas 7 and the holdingmember 2 is expressed by a value referred to as a thermal adaptationfactor. The thermal adaptation factor depends on the kind of cooling gasand the surface condition of the member (state of contamination etc.).The same can be applied to the heat transfer between the substrate 1 andthe cooling gas 7. Helium is used as the cooling gas 7 because heliumdoes not affect the etching characteristic when it leaks, and becausethe supplying or exhausting time for the cooling gas 7 is shorter thanfor other gases. However, other gases, such as nitrogen, argon, and anetching gas may be used, although the cooling efficiency is changed. Thecooling gas is not specially limited to these examples.

As described above, the substrate 1 is sufficiently cooled through useof the cooling gas. Further, the substrate contacts to the holdingmember 2 only at the protruding portion 3. Accordingly, foreignsubstances produced by contacting the back surface of the substrate toanother member are likely to attach only to the portions on the backsurface of the substrate corresponding to the protruding portion 3. In acase where the substrate 1 has a larger area than the holding member 2and a part of the surface of the holding member sticks out beyond theedge of the substrate 1 shown in FIG. 2, plasma is irradiated on theexposed projecting surface to etch that surface and the etching reactionproducts from the substrate 1 are attached to the projecting surface.Thereby, foreign substances attach to the top side surface of thesubstrate 1 through the sticking surface.

This is the reason why the diameter of the holding member 2 is smallerthan the diameter of the substrate 1. However, the effect of decreasingforeign substances on the back surface according to the presentinvention is not degraded even when the diameter of the holding member 2is larger than the diameter of the substrate 1.

FIG. 3 shows another form of the substrate holding system 9 according tothe present invention. Although the embodiment in FIG. 3 is basicallythe same as that in FIG. 2, the embodiment in FIG. 3 has a pusher 19 fortransferring the substrate 1. The substrate 1 is transferred from theholding member 2 by moving the pusher 19 upward and downward. The pusher19 has to be moved upward and downward for every treatment. That is, thepusher needs to be moved independently of the holding member 2.Therefore, there is a need to provide a gap between the holding member 2and the pusher 19. The cooling gas 7 leaks through the gap. The leakageamount of cooling gas 7 needs to be suppressed as much as possible. Inorder to realize this, an inner side protruded portion 20 having asurface nearly the same height or the same height as that of theprotruding portion 3 is provided around the pusher 19. Since the surfaceis flat and contacts the substrate 1, the leakage amount of the coolinggas can be suppressed within an allowable amount. The reasons why thepusher is provided in the center of the protruded portion 20 are thefollowing three.

(1) For exhausting the excess gas,

(2) for exhausting the foreign substances produced at the pusher portionwith the gas flow, and

(3) to prevent an abnormal discharge.

The occurrence of an abnormal discharge depends on the kind of gasesused, the pressure of the environment, the gap distance applying voltageand the voltage. In a case where the pusher is placed, for example, in acooling gas environment, the gap distance applying voltage needs to be0.16 to 0.2 mm, when the pressure of the cooling gas environment is 8 to10 Torrs (mHg) and the voltage for electrostatic adhering is 450 to 700V. However, forming such a gap is difficult. In the case of theembodiment according to the present invention, the pressure of theenvironment containing the pusher 19 can be made very much lower thanthe pressure at which discharge is easy to occur, and an abnormaldischarge can be prevented from occurring even when the pressure of theenvironment containing the pusher 19 is higher than the pressure in theetching chamber of 3 to 5 mm Torrs by the pressure difference forincreasing conductance, for example, 10 mmTorrs (1/10² mmHg) and the gapdistance is approximately 1 mm.

FIG. 4 is a view of the substrate holding system 9 in FIG. 3 forremoving the substrate 1, looking down from an upper side. A feeding andexhausting hole 21 for the cooling gas 7 is provided in the center ofthe holding member 2, and the pushers 19 and the inner side protrudingportions 20 are arranged around the feeding and exhausting hole 21. Theinner side protruding portions 20 also serve as supports against thebending of the substrate 1.

Although the inner side protruding portion 20 is round-shaped in FIG. 4,the shape is not limited to a round-shape. FIG. 5 shows an embodiment ofa substrate holding system 9 which is ring-shaped. There are provided inthe ring-shaped protruding portions 22 a temperature sensor 23 for thesubstrate 1, a substrate detecting sensor 24 for detecting the existenceof the substrate, an earth terminal 25 for bringing the potential of thesubstrate 1 to earth potential, in addition to the pusher 19. In orderto perform speedy feeding and exhausting of the cooling gas 7 to theindented portion 8, parts of the ring-shaped protruding portion 22 arecut away to allow the cooling gas 7 to pass through the parts easily.

In an apparatus using plasma, employing a fluorescent thermometer as thetemperature sensor 23 eliminates the problem of noise. An example of asubstrate detecting sensor 24 is an optical fiber through which a laserbeam is introduced to irradiate the back surface of the substrate 1. Thepresence of the substrate 1 is detected by the existence of reflectedlight. Since the output of the temperature sensor 23 changes dependingon the presence of the substrate 1, the change can be used in detectingpresence of the substrate 1.

The earth terminal is used before pushing up the substrate 1, which hasbeen electrostatically fixed, by using the pusher 19. While thereremains an adhering force on the substrate 1 which has beenelectrostatically fixed, the pusher cannot be used. Therefore, in orderto shorten the waiting time, there are some cases where the substrate 1is required to be grounded. By moving the earth terminal 25 upward anddownward so as to contact the substrate 1, the potential Of thesubstrate 1 is neutralized. Although the earth terminal 25 is made of anelectrically conductive material, it is effective to employ siliconcarbide having a much larger resistivity than general metals to avoid anabnormal discharge during plasma treatment. Further, it is possible thatthe function of grounding may be incorporated in the pusher 19.

Although various kinds of sensors are arranged on a single holdingmember in FIG. 5, the sensors can be used separately without degradingthe object of the present invention.

By employing the substrate holding system 9 according to the presentinvention, the amount of foreign substances attaching to the backsurface of the substrate 1 is decreased. Further, by holding thesubstrate 1 during treatment using the substrate holding system, it ispossible to prevent foreign substances carried on the back surface fromattaching to the top surface of another adjacent substrate, which couldcontaminate the substrate by foreign substances melted or detached fromthe back surface.

FIG. 6 shows a further form of the substrate holding system 9 accordingto the present invention. The holding member 2 has island-shapedprotruding portions 22A, 22B arraying concentrically. In this embodimenta substrate is supported with three concentric portions, the protrudingportion 3 in the peripheral area, and the island-shaped protrudingportions 22A and 22B. This configuration is especially effective whenthe diameter of the substrate 1 is large.

FIG. 7 shows another embodiment according to the present invention. FIG.7 is a detailed cross-sectional view showing a substrate holding system9 of a microwave plasma etching apparatus to be described later. Aninsulating film for electrostatic adhering is coated on the top surfaceof a head portion 61. A weir 62 a for contacting and fixing a substrate1 is provided at the periphery of the substrate, and a weir 62 b and aweir 62 c are provided inwardly of the weir 62 a. A hole 66 penetratingto the back surface of a mounting table is provided in the center of theweir 62 c. A space 64 for containing coolant is provided inside the headportion 61, and a passage capable of feeding and exhausting the coolantis provided in communication with the space 64. A shaft 63 secured tothe head portion 61 is provided near the center of the substrate holdingsystem 9, and a guiding passage for introducing cooling gas is providedinside the shaft. A pusher mechanism 65 for transporting a substrate isprovided in engaging relationship with the hole 66 described above. Acover 67 is placed in the outer peripheral portion of the penetratinghole 66 on the back of the mounting table. A susceptor 68 serves as acover for head portion 61 to protect the head portion 61 during etchingand to insulate the side surface of the head portion from thesurrounding electrical space.

In a case where a substrate 1 (wafer) is treated in the embodiment inFIG. 7, the substrate 1 is introduced into a treating chamber usingloading means (not shown) under a vacuum condition, the substrate 1 ismounted on a mounting table 9 having its temperature controlled inadvance with a coolant, current is supplied to an electromagnetic coil4A (see FIG. 10) to form a given magnetic field, a treating gas isintroduced, current is supplied to a magnetron to generate microwaveenergy, the gas is turned into a plasma in the treating chamber by ECR(electron cyclotron resonance), and a DC circuit is formed by the plasmato produce an electrostatic adhering force. Then, a cooling gas iscaused to flow between the substrate 1 and the mounting table 9. Thecooling gas rapidly diffuses inside the gap, except for contact portionsthereby transferring the heat entering from the plasma into thesubstrate 1 (wafer) to a head portion of the holder by way of thecoolant. In order to extend the cooling effect up to the vicinity of theouter periphery of the substrate, the cooling gas is leaked to thetreating chamber through the outer periphery of the substrate. At thesame time, the cooling gas is exhausted to the back of the mountingtable as an excess gas through a penetrating hole 66 having adimensional relationship so as to leak the cooling gas actively. Sincethe gas between the substrate and the mounting table needs to bemaintained above a given pressure, gas is always supplied in an amountcorresponding to the leaked amount.

According to the embodiment, it is possible to provide a plasma treatingapparatus in which the amount of foreign substances transferred to theback surface of a substrate is decreased by decreasing the contact areabetween the substrate and the holder while maintaining the coolinggas-pressure required for cooling, and which has a good repeatability asa production apparatus, being capable of treating a substrate withplasma under a condition of controlling the substrate temperature, andhaving excellent productivity.

Further, it is possible to provide a plasma treating apparatus in whichthe foreign substances produced in the pusher portion are transported tothe opposite side of the substrate by exhausting the excess cooling gasto the back of the mounting table (opposite side of the substrate) todecrease the amount of foreign substances attaching to the substrate;and concurrently, the gas is exhausted inside a cover provided on theback of the mounting table in the treating chamber to keep the pressureinside the cover higher than the pressure in the treating chamber and toprevent the reaction products from attaching to the mechanisms of themounting table, and of which the characteristic is small time-varying.

Helium is generally used as the cooling gas here. Although in thepresent invention the cooling gas leaks into the treating chamber byseveral ccm (cubic centimeter per minute) to 10 cam, it has beenconfirmed by experiment that the leakage amount does not affect theprocess, since the amount is 1/100 to 1/several tenths of the suppliedamount of process gas.

Although the present invention has been described in each of the aboveembodiments while taking substrate cooling into consideration, it isunderstood that there is no substantial difference in a case of heatinga substrate, since the only difference is that the temperature of theholding member is kept higher than the temperature of the substrate.

According to the present invention, a substrate can be certainly cooledand at the same time the amount of foreign substances attached to theback surface of the substrate can be decreased. Further, the amount offoreign substances attached to the top surface of the substrate also canbe decreased since the substrate is fixed using electrostatic adhesionand there is no need to use any substrate fixing hardware which willcontact the substrate on the top surface of the substrate. Furthermore,substrate treatment on the top surface of a substrate can be performedthroughout the surface of the substrate since there is no obstacle, suchas substrate fixing hardware. Therewith, the yield of production insubstrate treatment can be improved by decreasing the amount of foreignsubstances on the back surface. The yield of production can be furtherimproved and the number of device chips obtained from a single substratealso can be increased by decreasing the amount of foreign substancesattached to the top surface of the substrate.

Damage to the substrate such as results from use of a conventionalelectrostatic adhering electrode is not caused in the present invention,which improves the yield of production.

Another embodiment of the present invention will be described in detailbelow, referring to the drawings.

FIG. 9 shows another embodiment in accordance with the presentinvention. In FIG. 9, a substrate 1 is held on a dielectric material 18formed on a holding member 2. Under the holding member 2, an insulatingmember 40 and a base 41 are placed and supported with a shaft 63. In theholding member 2, a coolant flow passage 42 for conducting a coolant tocontrol the temperature of the substrate 1 is formed. In order to supplythe coolant to the coolant flow passage 42, a through hole penetratingthrough the base 41 and the insulating member 40 is provided and acoolant supply portion 43 is also provided. A pusher 19 is inserted in athrough hole penetrating through the holding member 2, the insulatingmember 40 and the base 41, the side surface of the through hole beingformed of an insulating pipe 44. The pusher 19 is guided with a guide 45provided around the shaft 63, being moved in the direction of the shaft63 with an upward and downward drive mechanism, which is not shown inthe figure, to transport the substrate 1. A high frequency supplyingshaft 47 is installed inside the shaft 63 through an insulating material46, the high frequency supplying shaft 47 being pipe-shaped, and theinside of the high frequency shaft forms a substrate cooling gas feedinghole 21. The insulating material 46 penetrates from the base 41 to theinsulating member 40. The high frequency supplying shaft 47 penetratesfrom the insulating member 40 to the holding member 2, one end (lowerside in FIG. 9) of the high frequency supplying shaft 47 being connectedto a high voltage power source, which is not shown in the figure, forapplying a high voltage to hold the substrate 1 to the dielectricmaterial 18 by electrostatic adhesion and to a power source for applyinga high frequency bias to the substrate 1. A substrate detecting sensor24 for detecting the presence or absence of a substrate by detecting thetemperature of the substrate is installed in FIG. 9. In this position, asubstrate detector which operates to detect cooling gas pressure insteadof detecting the substrate temperature may be also employed. In thiscase, the pressure sensor is placed at the top end of the pin in thesubstrate detecting sensor 24, and an output signal wire from thepressure sensor is passed through the inside of the pin to be connectedto a signal processor. Since the pressure in the space around the topend of the pin in the substrate detecting sensor 24 is high when asubstrate is present and is low when a substrate is absent, the signalprocessor detects the presence or absence of the substrate by judgingwhether or not the pressure signal from the pressure sensor exceeds avalue corresponding to a preset pressure. A susceptor 36 serving as acover for the dielectric material 18 and the holding member 2 is placedon the outer peripheral portion of the substrate 1 to cause the gas flowfor substrate etching to be uniform. The inner peripheral surface of thesusceptor 36 is perpendicular to the back surface of the substrate 1.The susceptor 36 is formed of an electrically insulating material, suchas alumina, covering the outer surrounding surface of the holding member2, the insulating member 40 and the base 41.

The substrate holding system shown in FIG. 9 is used in, for example, aplasma environment as shown in FIG. 10. FIG. 11 is an enlargedcross-sectional view of the peripheral portion of the substrate 1.Although FIG. 10 is a schematic view of a microwave plasma etchingapparatus, explanation will be made below on a case where the substrateholding system according to the present invention is applied to anetching apparatus.

The vacuum chamber 27 is connected to another vacuum chamber to load andunload the substrate 1 from and into the atmospheric environment througha valve. The substrate 1 loaded into the vacuum chamber 27 through thesubstrate loading mechanism is transported at a transporting levelindicated by a two-dot chain line in FIG. 10. Therefore, the substrateholding system 9 is lowered to the transporting level. The substrate 1is transported to and mounted on the dielectric material surface 18 bymoving the pusher 19 upward and downward at this level. The coolant tocontrol the temperature of the substrate 1 is introduced into thecoolant flow passage 42 from the coolant supply portion 43 through acoolant temperature controller which is separately provided and thecoolant is recirculated in the coolant flow passage to control thetemperature of the holding member 2 and the dielectric material 18 at agiven temperature. When the substrate 1 is mounted on the substrateholding system 9, a laser beam introduced from the substrate detectingsensor 24 is reflected on the back surface of the substrate, thereflected light being detected as a signal which confirms the mountingof the substrate 1. The temperature of the substrate is started to bedetected using a substrate temperature detector (fluorescentthermometer), which is not shown in FIG. 9, installed in the same manneras the substrate detecting sensor 24. When the etching gas 48 issupplied and the microwave energy is introduced from the microwavegenerator 26 through the waveguide 14 14, discharging is started. Inthis state, a direct current for electrostatic adhesion is supplied fromthe direct current power source 13, an electric circuit forelectrostatic adhesion is formed through the plasma 16, and thesubstrate 1 is attracted to the dielectric material 18. Then, whenhelium gas is supplied from the gas feeding hole 21 substratetemperature control through the helium gas is carried out. In thisstate, since the preparation for etching is completed, etching isstarted by setting the microwave at a given value and applying the highfrequency voltage. After completion of the etching treatment, supply ofthe high frequency voltage is stopped. At this time, the plasma stillremains. That is, the substrate is still attracted electrostatically.The supply of etching gas is stopped and a, non-etching gas, such asargon gas, instead of the etching gas, is introduced, depending on thesituation, to remove the charge accumulated during electrostaticadhering. In the meanwhile, the supply of helium gas is stopped, and theforce to lift up the substrate 1 from the back surface of the substrate1 is not applied. After completion of discharging, the supply of argongas is stopped, and the direct current for electrostatic adhesion isstopped. After exhausting the etching gas and the gas for discharge toachieve a high vacuum state, downward movement of the substrate holdingsystem 9 and the process for unloading the substrate 1 are started. Theunloading process is performed in the inverse process of the loadingprocess. A new substrate is loaded for the next etching. Then, etchingis carried out in the same manner as above.

Although the reaction products (gas) produced by the etching gas andetching on the surface of the substrate is distributed in anapproximately uniform density over the surface of the substrate 1, theetching characteristic in the peripheral portion may be different fromthat in the central portion since in the outer peripheral portion of thesubstrate the portion to produce the reaction products does not existoutside the substrate and the flow boundary of gas flow abruptlychanges. Therefore, in accordance with the present invention, thesusceptor 36 is placed approximately at the same level as the substrate1 to prevent any abrupt change in the gas flow. The flow of the etchinggas and the reaction products is directed slightly upward due to theexistence of the surface of the susceptor 36, and a stagnant effect ofthe etching gas and the reaction products takes place and causes aphenomena as if there is an etching reaction portion in the outerperipheral portion of the substrate. Therefore, etching is uniformlyperformed in the peripheral portion of the substrate.

In addition to the above, there is an effect that, since the peripheryof the substrate 1 is in a state of being contained in the susceptor 36and the side wall 36A of the susceptor 36 restricts the substrate 1 fromshifting to any significant extent, it is possible to avoid thesituation where the substrate cannot be transported and the vacuum ofthe etching chamber has to be broken even when the electrostaticadhering force is removed with some abnormal state and the substrate 1is moved by the pressure of the helium gas supplied to the back surfaceof the substrate 1. At this time, the substrate 1 does not ride on thehorizontal surface of the susceptor 36 even when the substrate 1 slides,because the inner surface 36A of the susceptor 36 facing the outerperipheral surface of the substrate 1 is nearly vertical. This case isdifferent from a case where the surface of the susceptor 36 istaper-shaped.

Description will be made below on the gap between the back surface ofthe substrate 1 and the susceptor 16.

On the substrate etching surface side, the plasma 16 is generated andthe etching gas and the reaction products are flowing. Therefore, whenthere is a gap between the back surface of the substrate 1 and thesusceptor 36, the etching gas and the reaction products enter into thegap and are accumulated in the back surface of the substrate. They formforeign substances. This is not desirable, because the product yield ofthe etching process decreases. On the other hand, when the gap betweenthem is decreased so as to be as small as possible, the etching gas andthe reaction products are decreased to enter the gap and the foreignsubstances accumulated in the back surface of the substrate can bedeceased. According to the result of another experiment, the effectdescribed above has been effective when the gap is less than 0.3 mm.

The etching treatment is performed while applying the high frequencyvoltage to the substrate 1. At this time, there are some cases where anabnormal discharge takes place between the holding member 2 to which thehigh frequency voltage is directly applied and the base 41. When theabnormal discharge occurs, the high frequency voltage is not correctlyapplied to the substrate 1, and the etching itself becomes abnormal.This is not limited to etching, but can be said generally of the type ofsubstrate treating apparatus in which plasma is generated using a highfrequency voltage. In order to prevent such phenomena, in the substrateholding system according to the present invention, the base 41, being ata different electric potential from the high frequency voltage appliedportion, is specially isolated by inserting the insulating pipe 44.Thereby, the abnormal discharge can be prevented.

Description will be made on transportation of the substrate 1. Charge isaccumulated on the substrate 1 while it is electrostatically fixed onthe holder. The charge has the capability of adhering the substrate 1 tothe dielectric material 18, and so the substrate 1 is electrostaticallyattracted to the dielectric thin film even when the direct current powersource 13 for electrostatic adhesion is switched off. Therefore,transportation of the substrate 1 has to be delayed until theaccumulated charge disappears. There is an additional problem ofdetermining whether the accumulated charge is present or absent. Inorder to solve this problem, the pusher 19 is made of a material havinga small conductivity, such as silicon carbonate, as shown in FIG. 12. Bydoing so, the accumulated charge flows to a grounded line through thepusher 19 to cause the charge to disappear. Thereby, the problem oftransporting the substrate can be avoided and a reliable substratetransportation can be realized. The grounded circuit connected to thepusher 19 may be disconnected during generation of the plasma. It ispreferable to employ this technique when the grounded line and the highfrequency applied portion are placed near each other and an abnormaldischarge takes place.

Although the substrate 1 is transported with upward/downward movement ofthe pusher 19, an abnormal state occurs if the substrate is vibratedduring transporting. Therefore, the pusher 19 has to move smoothly. Inorder to guide the pusher with certainty, in accordance with the presentinvention, the guide 45 is provided on the shaft 63. By doing this, thelength of the pusher 19 does not become excessively long and a highlyreliable transportation can be realized.

As described above, the elements of a highly reliable substrate holdingsystem have been explained. Description will be made below on thesolution of the problem in a case where the substrate transporting levelis different from the level of the substrate treating position (thesubstrate position corresponding to the position illustrated in FIG.10).

FIG. 13 shows the comprehensive construction of a substrate holdingsystem. The upper portion of the system is nearly the same as in FIG. 9.The main difference from FIG. 9 is that the outer side surface of theholding member 2 applied with the high frequency voltage is covered withan insulating member 40. By doing so, the distance between the portionto which the high frequency voltage is applied and the grounded portionbecomes long and the preventive effect against abnormal discharge can beimproved.

In order to travel upward and downward between the substratetransporting position and the substrate etching position, a bellows 50is provided between the shaft 63 of the substrate holding system and theflange 49 in the present invention. The bellows 50 also serves as avacuum seal between the atmosphere and the etching chamber and isextended with a guide for the shaft 63 and an upward and downward drivemechanism installed in the atmospheric environment, which are not shownin FIG. 13. In accordance with the present invention the bellows isplaced between the shaft 63 and the flange 49 to minimize the diameterof the bellows 50. When the diameter of the bellows 50 is small, theforce loaded on the substrate transporting mechanism is also small andconsequently it is easy to make the upward and downward drive mechanismsimple and highly accurate. It is needless to say that the foreignsubstances produced by abrasion in the sliding portion are eliminatedand the reliability of the vacuum seal is improved in comparison to acase of employing a sliding portion using an elastomer seal.

Although by employing such a construction the substrate holding systemis moved upward and downward, exposure of the bellows 50, the shaft 63,and the pusher 19 to the plasma is not preferable from the point of viewof foreign substances formed by attached etching products or the plasmaresistivity of the materials. Therefore, in the present invention,cylindrical covers 67A and 67B engaging with each other are provided onthe base 41 and on the flange 49. The covers 67A, 67B engage with eachother and have such dimensions that the contact is maintained even whenthe substrate holding system moves upward and downward. The covers 67Aand 67B are kept at a grounded electric potential, and so the membersinside the covers are always isolated from the plasma so as to beprotected from contamination.

As described in the above embodiment, according to the presentinvention, a substrate holding system and a method of holding asubstrate having less foreign substances and which is capable ofperforming uniform etching can be attained.

It is understood that the present invention is not limited to thedescribed etching apparatus, but is widely applicable to varioussubstrate treating apparatus and treating holding of a substrate(treated object) with electrostatic adhesion.

In looking at FIG. 9 or FIG. 13 from the point of view of manufacture ofthe substrate holding system, it is difficult to manufacture the holdingmember 2 since it has the coolant flow passage. As a matter of course,it is possible to obtain a member having the same effect bymanufacturing the holding member 2 by dividing it into two parts throughmachining, as shown in FIG. 9, jointing the parts to each other, andsealing the coolant using an elastomer seal. However, in this case,there arise such problems as an increase in complexity and a decrease inreliability due to extra jointing portions or extra volume beingrequired, since a sealing surface 55 is required, and a seal is requiredin each hole of the parts when a through hole (for example, the holeinserted with the insulating pipe 44 in FIG. 9) is provided in theholding member 2, as shown in FIG. 9.

Therefore, the present invention employs a manufacturing method wherethe holding member 2 is formed in a one-piece structure.

In the present invention, a lost wax technique is employed as a methodto solve this problem. FIG. 14 shows this embodiment. First, a member 51having the same shape as the coolant flow passage 42 is fabricated usingwax. Next, a mold having the same shape as the outer shape of theholding member 2 is prepared, the flow passage mold made of wax beingplaced inside the mold, and then casting is performed. After removingthe wax, the holding member 2 is completed.

FIG. 15 and FIG. 16 show another embodiment according to the presentinvention. In this embodiment, a metallic member 52, which is machinedto form the coolant flow passage 42 in advance, and a holding member 53are coupled with each other through a jointing material 54. When theholding member is made of aluminum or an aluminum alloy, an aluminumalloy having a low melting temperature (for example, a silicon containedaluminum alloy) is used for the jointing material 54. Then, the members52, 53 are heated up to approximately 600° C. in a vacuum environmentwith pressing, the jointing material 54 having a low melting temperaturebeing melted and reacting with the metallic members 52 and 53 to bejointed to each other. Since the sealing surface 55 shown in FIG. 16 canbe certainly jointed by employing the diffusion welding method, thethrough hole 66 can be made without any special consideration. Since inthe welding process many sets of members, not limited one set, can bewelded at a time, there is no problem in cost performance bymanufacturing a lot of the metallic members 52, 53 in advance andwelding them at the same time.

As described above, according to the present invention, since substrateholding by electrostatic adhesion can be certainly preformed withoutusing a member, such as a weight, on the substrate surface forpreventing sliding during substrate transporting or for preventinglift-up due to gas pressure on the back surface of the substrate, thereis an effect that production of foreign substances during substrateetching can be decreased and the production yield of the substrate canbe expected to be improved. Further, since the operable period betweencleaning services of the substrate etching apparatus for removing theforeign substances is lengthened, there is an effect that theoperability of the apparatus can be expected to be improved.Furthermore, since the surface of the outer peripheral portion of thesubstrate is nearly at the same level as the surface of the substrate inorder to make the gas flow in the surface of the substrate uniform,there is an effect that the substrate etching can be performed withexcellent uniformity over the surface. Still further, since no elastomerseal is required for coolant sealing in forming the substrate holdingsystem, there is an effect that the substrate holding system can beeasily manufactured.

We claim:
 1. An apparatus for processing a substrate comprising: aholder; electrostatic attraction means for fixing said substrate to saidholder so that at least a portion of a back surface of the substratecontacts contact portions of the holder; means for providing a back sidegas between the substrate back surface and said holder; and means forlimiting the adherence to the substrate back surface of foreignsubstances caused by contact between the substrate back surface and thecontact portions of the holder, and for preventing the deformation ofthe substrate by the back side gas.
 2. An apparatus for processing asubstrate comprising: a holder; electrostatic attraction structure whichfixes said substrate to said holder so that at least a portion of a backsurface of the substrate contacts contact portions of the holder; and agas supply which provides a back side gas between the substrate backsurface and said holder through a first hole at the center of saidholder; an area of said contact portions being chosen to limit theadherence to the substrate back surface of foreign substances caused bycontact between the substrate back surface and the contact portions ofthe holder, and to prevent the deformation of the substrate by the backside gas.
 3. An apparatus for processing a substrate according to claim2, wherein a second hole is provided apart from said first hole at thecenter in said holder, wherein a push pin is located in said secondhole.
 4. An apparatus for processing a substrate comprising: a holder;an electrostatic attraction structure which fixes said substrate to saidholder so that at least a portion of a back surface of the substratecontacts contact portions of the holder; and a gas supply which providesa back side gas between the substrate back surface and said holderthrough a hole at the center of said holder, wherein an area of saidcontact portions is limited so as to be as small as necessary to reducethe adherence to the substrate back surface of foreign substances, andto prevent the deformation of said substrate due to a gas pressure ofsaid back side gas being suppressed.
 5. An apparatus to process asubstrate comprising: a holder, wherein said substrate is fixed to saidholder by electrostatic attraction so that at least a portion of a backsurface of the substrate contacts contact portion of the holder; and agap between the substrate and the holder to provide a back side gasbetween the substrate back surface and said holder; and wherein an areaof said contact portions is set to be sufficiently small to limit theadherence to the substrate back surface of foreign substances caused bycontact between the substrate back surface and the contact portions ofthe holder, and to be sufficiently large to prevent the deformation ofthe substance by the back side gas.
 6. An apparatus to process asubstrate comprising: a holder which fixes said substrate to a firstsurface of said holder by electrostatic attraction so that at least aportion of a back surface of the substrate contacts contact portions ofthe holder; and a gas supply which provides a back side gas between thesubstrate back surface and said holder through a first hole in saidholder; an area of said contact portions being chosen to limit theadherence to the substrate back surface of foreign substances caused bycontact between the substrate back surface and the contact portions ofthe holder, and to prevent the deformation of the substrate by the backside gas.
 7. An apparatus to process a substrate according to claim 6,wherein said first hole is located at the center of said holder andwherein said electrostatic attraction is generated by a dielectricmaterial located on said first surface of said holder.
 8. An apparatusto process a substrate according to claim 7, wherein a second hole isprovided apart from said first hole at the center in said holder,wherein a push pin is located in said second hole.
 9. An apparatus toprocess a substrate comprising: a holder which fixes said substrate to afirst surface of said holder by electrostatic attraction so that atleast a portion of a back surface of the substrate contacts contactportions of the holder; and a gas supply which provides a back side gasbetween the substrate back surface and said holder through a hole insaid holder, wherein an area of said contact portions is limited so asto be as small as necessary to reduce the adherence to the substrateback surface of foreign substances, and to prevent the deformation ofsaid substrate due to a gas pressure of said back side gas beingsuppressed.
 10. An apparatus to process a substrate according to claim9, wherein said first hole is located at the center of said holder andwherein said electrostatic attraction is generated by a dielectricmaterial located on said first surface of said holder.
 11. An apparatusto process a substrate according to claim 10, wherein a second hole isprovided apart from said first hole at the center in said holder,wherein a push pin is located in said second hole.